In the case of an image reflected in a plane mirror, because the light beams of the reflected light occurring at the surface of the mirror appear to come from a direction extending into the interior of the mirror to the eyes of an observer, an image reflected in a plane mirror (a mirror image) is formed as a virtual image within the interior of the mirror (see, for example, Non-patent Reference No. 1).    Non-patent Reference No. 1—The definition of “virtual image” from the Wikipedia Website on the Internet, accessed on the Oct. 23, 2006, at: <URL:http://en.wikipedia.org/wiki/Virtual_image>